Semiconductor manufacturing involves highly complex techniques for integrating circuits into semiconductor materials. Due to the large number of processing steps and the decreasing size of semiconductor devices, the semiconductor manufacturing process is prone to processing defects that decrease device yields. Inspection procedures used to detect and eliminate these processing defects from the processing steps are therefore critical for maintaining high yielding production processes. Since the inspection procedures are an integral and significant part of the manufacturing process, the semiconductor industry constantly seeks more accurate and efficient inspection techniques.
Currently, typical microscopic inspection systems utilize a single detector array to inspect semiconductor wafers. The detector arrays may contain a variety of sensor-element (pixel) densities. For example, detector arrays having a 2048×512 array of pixels are available. To inspect a wafer, a detector array is typically raster scanned over the patterned wafer's surface under high magnification. Unfortunately, scanning wafers line-by-line is time consuming, especially when the time required for changing the relative directions of the detector arrays over the wafer is taken into account. Typically, the wafer is attached to an x,y stage and driven under the microscope. During a swath across the wafer, the stage must accelerate to a constant speed, scan the swath of patterned surface to be inspected, decelerate to a stop, move up one field of view in the transverse direction, and accelerate to the constant velocity again for another swath. The overhead of non-swathing the patterned surface can be a significant fraction of the total wafer inspection time. For example, a magnification of 100× with a 20 um sized pixel and 2048 detector elements would produce a scan width of 0.41 mm and would require 732 swaths to cover a standard 300 mm diameter semiconductor wafer. If overhead of each swath were 1 second, then the inspection time would be extended by over 12 minutes for each wafer. Therefore, microscopic inspection of wafers reduces the throughput of semiconductor manufacturing. One possible solution is to create larger sized detector arrays such that fewer scanning passes of the detector array over the wafer are required. Unfortunately, larger detector arrays with no defective pixels are very difficult to fabricate because yields are small with physically large devices. Another possible solution is to run the current detectors at higher speeds. However, it is difficult to obtain much improvement from the current state-of-the-art using this strategy because the detectors create a greater amount of noise at higher speeds, thereby diminishing the signal-to-noise ratio. This would also not help the scanning overhead time.
In view of the foregoing, a microscopic inspection system that is able to operate at higher speeds such that higher manufacturing throughputs can be achieved, would be desirable.